This is a new application for a research training program in Molecular Hematology submitted by a group of investigators who are all on the faculty of Harvard Medical School and work either within HMS or one of its affiliated hospitals or research centers. The grant grew out of a merger between two existing Hematology research training programs centered at the Beth Israel and Brigham and Women's Hospitals and is an attempt to bring together many of the scientists at HMS who work in areas germane to Hematology and are interested in training the postdoctoral fellows to be supported by the Institutional NRSA. The trainees will be selected by a Steering Committee from graduates of clinical training programs at the BWH/MGH and BIH, as well as from the applicants who apply directly-to programs for research training and those nominated by laboratory-preceptors. The overall goal of the program is to train physicians and other interested biomedical)scientists for a career in Hematology Research. Funds are also requested to support the pre-doctoral training of graduate students working in preceptor laboratories and for two Minority summer students. The major areas of Hematology research, including Red Cell Membranes, Hemoglobinopathies, Hematopoiesis, Immunology, Hemostasis/Thrombosis and Vascular Biology, are represented in the grant. Special attention has been paid to a rigorous selection process, adequate mentoring, excellent preceptors and promoting scientific interactions between participating laboratories. In this way the program hopes to take full advantage of the superb resources present at Harvard Medical School and provide optimal training for grant appointees. The merged proposal replaces the existing postdoctoral training positions on the two formerly independent grants.